84321I Datasheet, PDF (13/18 Pages) Integrated Device Technology – 260MHz, Crystal-to-3.3V Differential

3. Calculations and Equations.
The purpose of this section is to derive the power dissipated into the load.
LVPECL output driver circuit and termination are shown in Figure 6.
84321I DATA SHEET
FIGURE 6. LVPECL DRIVER CIRCUIT AND TERMINATION
To calculate worst case power dissipation into the load, use the following equations which assume a 50Ω load, and a
termination
voltage of V_CCO- 2V.
• For logic high, VOUT = V_{OH_MAX} = V_{CCO_MAX} – 0.9V
(V_{CCO_MAX} - V_{OH_MAX}⁾ = 0.9V
• For logic low, VOUT = V_{OL_MAX} = V_{CCO_MAX} – 1.7V
(V_{CCO_MAX} - V_{OL_MAX}⁾ = 1.7V
Pd_H is power dissipation when the output drives high.
Pd_L is the power dissipation when the output drives low.
Pd_H = [(V_{OH_MAX} – (V_{CCO_MAX} - 2V))/R_L] * (V_{CCO_MAX} - V_{OH_MAX}) = [(2V - (V_{CCO_MAX} - V_{OH_MAX}^))/R_L] * (V_{CCO_MAX} - V_{OH_MAX}) =
[(2V - 0.9V)/50Ω) * 0.9V = 19.8.mW
Pd_L = [(V_{OL_MAX} – (V_{CCO_MAX} - 2V))/R_L] * (V_{CCO_MAX} - V_{OL_MAX}) = [(2V - (V_{CCO_MAX} - V_{OL_MAX}^))/R_L] * (V_{CCO_MAX} - V_{OL_MAX}) =
[(2V - 1.7V)/50Ω) * 1.7V = 10.2mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 30mW
REVISION B 11/5/15
13
260MHZ, CRYSTAL-TO-3.3V DIFFERENTIAL
LVPECL FREQUENCY SYNTHESIZER